Biomedical Engineering Reference
In-Depth Information
nanostructures produced
[5,6]
. It was shown using FESEM that a nanotubular amorphous fluoride con-
taining TiO
2
layer could be produced on a micro-roughened titanium surface
[6]
. Potential benefits of
such a surface include increased surface area that could be used for drug delivery and growth factors
as well as better matched interfacial elastic modulus that should enhance osseointegration as compared
with conventional dental and orthopedic implants with smooth or acid-etched surfaces
[6]
. This latter
work presents a good example of where multiple characterization techniques can be useful to eluci-
date information and understand new material developments. Given the potential benefits to patients
of more readily accepted and longer lasting implants, the importance of full characterization of pos-
sible new dental materials or processes can be understood. In the work of Kim et al.
[6]
, an FESEM
(S-4700, Hitachi, Japan) with an energy dispersive X-ray spectrometer (EDS), a transmission electron
microscope (TEM), an X-ray photoemission spectrometer (XPS), an X-ray diffractometer (XRD), a
profilometer, a contact angle measurement device, a nanoindentation device, and a scratch resistance
measurement device were used to characterize the nanoporous layer. A machine smoothened and a
restorable blast media roughened surface were anodized in order to produce a nanotubular surface.
Such a TiO
2
layer has been reported to efficiently improve the cellular activities on titanium
in vitro
and bone-implant bonding properties
in vivo
. Roughened implants affect the rate of osseointegration
and biomechanical fixation. Roughened titanium dental implants exhibit higher bone-implant contact
area and greater pullout strengths. From the FESEM images it was found that the nanotubes, of about
100 nm in diameter and 500 nm in length, were closed at the substrate end, open at the end exposed to
electrolyte, and were attached to each other via their side walls (
Figure 18.1
).
18.1.2
Scanning Probe Microscopy
Scanning probe microscopy (SPM) is a general term that covers a wide range of techniques within
which a physical probe is passed over a surface via piezoelectric actuators in order to reproduce the
surface features. The first of these, scanning tunneling microscopy (STM), techniques was invented
in 1981.
18.1.2.1 Scanning Tunneling Microscope
In 1986 Binnig and Rohrer won the Nobel Prize in Physics for their work to develop the STM tech-
nique for imaging surfaces with atomic precision
[7]
. An STM consists of a tip (typically tungsten,
platinum-iridium, gold, or carbon nanotube (CNT)) sharpened to one atom width which is scanned
over the surface to be measured. Piezoelectric actuators are used to control the scanning of the tip in
the
x
,
y
(lateral), and
z
(normal) directions with respect to the surface. This technique is used to image
conductive or semiconductive materials' surfaces and provides the highest resolution of many of the
surface imaging techniques. Well-operated and constructed STMs can be used to provide for 0.1 nm
lateral resolution and 0.01 nm depth resolution. In order to achieve these resolutions, vibration control
of the sample and within the measurement system is crucial. Spring-based and other vibration isola-
tion systems are often used for this purpose. The sample can be measured in air, liquid, or alternate
gas environments. However, to avoid sample contamination, to achieve more stable operating condi-
tions, and to achieve higher resolutions, the sample is often measured under vacuum.
During operation of an STM the tip is brought close to the surface under coarse control and then
to an equilibrium position between tip attraction and repulsion that is typically within a range of
4-7 Å for the surfaces. When the conducting tip is brought this close to the surface a bias between the
two can allow electrons to tunnel between them. At low voltages, this current provides a record of the
